What does the name Ryuko mean?

Ryuko is a common Japanese name (male version, female version is spelled with 2 u's, like Ryuuko).

The Japanese meaning behind Ryuko (both for male and female) can be either "dragon-spirited child" or just "dragon child".

Ryuko in Japanese kanji is shown as 竜子.

Ryu (and Ryuu) mean "dragon" and ko means "child"

Hope this helps (^_^)